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Catalytic enantioselective synthesis of atropisomeric biaryls by a cation-directed O-alkylation
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Catalytic enantioselective synthesis of atropisomeric biaryls by a cation-directed O-alkylation
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Catalytic enantioselective synthesis of atropisomeric biaryls by a cation-directed O-alkylation
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Journal Article
Catalytic enantioselective synthesis of atropisomeric biaryls by a cation-directed O-alkylation
2017
Overview
Axially chiral biaryls, as exemplified by 1,1′-bi-2-naphthol (BINOL), are key components of catalysts, natural products and medicines. These materials are synthesized conventionally in enantioenriched form through metal-mediated cross coupling,
de novo
construction of an aromatic ring, point-to-axial chirality transfer or an atropselective transformation of an existing biaryl. Here, we report a highly enantioselective organocatalytic method for the synthesis of atropisomeric biaryls by a cation-directed
O
-alkylation. Treatment of racemic 1-aryl-2-tetralones with a chiral quinidine-derived ammonium salt under basic conditions in the presence of an alkylating agent leads to atropselective
O
-alkylation with e.r. up to 98:2. Oxidation with DDQ gives access to
C
2
-symmetric and non-symmetric BINOL derivatives without compromising e.r. We propose that the chiral ammonium counterion differentiates between rapidly equilibrating atropisomeric enolates, leading to highly atropselective
O
-alkylation. This dynamic kinetic resolution process offers a general approach to the synthesis of enantioenriched atropisomeric materials.
A chiral ammonium salt mediates a dynamic kinetic resolution of racemic α-aryl ketones by atropselective
O
-alkylation. Oxidation with DDQ gives access to
C
2
-symmetric and non-symmetric BINOL derivatives in high yields and with high enantioselectivity.
